The impact of vitamin D supplementation on mortality rate and clinical outcomes of COVID-19 patients: A systematic review and meta-analysis

Background: Several studies have suggested the positive impact of vitamin D on patients infected with SARS-CoV-2. This systematic review aims to evaluate the effects of vitamin D supplementation on clinical outcomes and mortality rate of COVID-19 patients. Methods: A comprehensive search was conducted through the databases of PubMed, Scopus, Web of Knowledge, Embase, Ovid, and The Cochrane Library with no limitation in time and language, until December 16, 2020. The results were screened based on their accordance with the subject. Two independent reviewers selected the eligible studies and the outcomes of interest were extracted. Using the Joanna Briggs Institute (JBI) Critical Appraisal Tools for Randomized Controlled Trials (RCTs) and Quasi-Experimental Studies, the remaining results were appraised critically. Statistical analysis was performed using the Comprehensive Meta-Analysis (CMA) software version 2.0. Results: Of the 2311 results, 1305 duplicated results were removed. After screening the titles, abstracts, and the full-text articles of the remaining records, four studies and 259 patients were enrolled, including 139 patients in vitamin D intervention groups. In three of the studies, the patients9 survival and mortality rate were evaluated. The pooled analysis of these studies showed a significantly lower mortality rate among the intervention groups (10.56%) compared with the control groups (23.88%) (OR = 0.264, 95% CI = 0.099-0.708, p-value = 0.008). Two of the studies reported the clinical outcomes based on the World Health Organization9s Ordinal Scale for Clinical Improvement (OSCI) score for COVID-19, where both of them showed a significant decrease in OSCI score in the vitamin D intervention groups. Additionally, One study reported a lower rate of intensive care unit (ICU) admission, and one study reported a significant decrease in serum levels of Fibrinogen. Conclusion: Prescribing vitamin D supplementation to patients with COVID-19 infection seems to decrease the mortality rate, the severity of the disease, and serum levels of the inflammatory markers. Further studies are needed to determine the ideal type, dosage and duration of supplementation.